In recent years the use of polymer based dental materials has gained in prominence, since these materials have improved physical and mechanical properties and provide dental restorations having superior durability. These materials have been found to be particularly useful as filled restorative materials, bonding agents, tissue scalers and orthodontic adhesives, particularly those materials, based upon polymerizable aromatic and aliphatic methacrylates, which polymerize in situ, most with the application of visual light.
The best properties in these types of materials have been obtained when the resin part of the composition is comprised of one or more of the following monomers: ##STR3## 2,2-bis[4'-(3"-methacroyl-2"-hydroxypropoxy)-phenyl]propane, known in industry as BIS-GMA, its adduct with various alkyl, iso, or diisocyanates, such as the adduct described by Waller, U.S. Pat. No. 3,629,187 and urethane dimethacrylates as are described, for example, in the U.S. Pat. Nos. 3,425,988; 3,709,866 and 3,629,187, and the like.
These products have a high molecular weight and viscosity and must be used in compositions with dilutants of low viscosity methacrylates, such as di- or tetraethylenglycol dimethacrylates, 1,6-hexandiol dimethacrylate or trimethylolpropane trimethacrylate. Most of these prepolymer type of monomers have a diphenylolpropane base. They possess in their molecular structure an aromatic double cycle and a strong ability to absorb curing light which makes deep curing difficult. The two hydroxyl groups in the molecule of BIS-GMA, which has a molecular weight of 512, make both the viscosity of the monomer and water absorption of the composition high. Synthesis of this pure monomer is also quite difficult.
In an attempt to improve methacrylate resin based dental materials, research efforts have been concentrated mainly on reducing their water absorption characteristics, minimizing their polymerization shrinkage and on improving their resistance to discoloration when exposed to sunlight. All of these properties depend upon the chemical structure of the monomer or monomers used in the formulation as well as their purity.
These research efforts have produced new formulations in the last few years, such as, for example, adducts of 3-methacroyl-2-hydroxypropylesters with diisocyanates of Orlowsky et al. U.S. Pat. No. 4,490,115. The efforts of Bowen to obtain methacrylate monomers with branched poly functional structure based on adduct of hydroxyethyl methacrylate and pyromellitic dianhydrid have permitted the creation of materials with improved adhesion to dentine and enamel. Industrial and Engineering Chemical Product Research and Development, pg 78-81 March 1984.
In addition to various aforementioned references polymeric dental materials have been described in the following U.S. Pat. Nos.: 3,066,112 (Bowen); 3,179,623 (Bowen); 3,194,783 (Bowen); 3,194,784 (Bowen); 3,539,533 (Lee II et al.); 3,541,068 (Taylor); 3,597,389 (Taylor); 3,721,644 (Stoffey et al.); 3,730,947 (Stoffey et al.); 3,751,399 (Lee Jr. et al.); 3,766,132 (Lee Jr. et al.); 3,774,305 (Stoffey et al.); 3,860,556 (Taylor); 3,862,920 (Foster et al.); 3,926,906 (Lee II et al.); 4,102,856 (Lee Jr.); 4,107,845 (Lee Jr. et al.); 4,490,115 (Orlowsky et al.); 4,544,359 (Waknine); 4,536,523 (Antonucci); 4,551,486 (Tateosian); 4,552,906 (Podszun); 4,553,940 (Koblitz et al.).